The present invention relates to devices for controlling positioning of an information recording and reproducing device and more particularly, to a device for controlling positioning of a magnetic disk device, an optical disk device or the like.
In an information recording and reproducing device such as a magnetic disk device or an optical disk device, its challenge is to realize a shortened access time by quickly positioning a head position to a target track position.
The access time in the disk device is determined by a time required for a speed control system to perform speed control for movement to the vicinity of the target track and by a time after change-over from-a speed control mode to a positioning control mode until the head is set at the target track position. The position control system immediately after the change-over from the speed control system to a position control system is controlled usually by a feedback compensator such as a PID compensator or a lead-lag compensator.
In a position control system disclosed in JP-A-3-23571, for the purpose of improving response characteristics by reducing an overshoot at a position after change-over from a speed control mode to a position follow-up control mode, a target position signal which exponentially approaches gradually a target track position, is added to a position deviation signal to follow up the position deviation signal to the exponentially-attenuating target position signal, thus improving response characteristics.
And the change-over from the speed control system to the position control system is carried out at a time point that a position deviation becomes a constant value or less.
The background art mentioned above has had a problem that, since the target position signal varies exponentially, only a lapse of an infinite time enables the target position signal to become zero, which results in that there is no guarantee that settling is completed in a finite settling time.
The background art has had another problem that, even when feedback compensation is tried to cause the position signal to follow up a change in the target position signal, a follow-up lag causes a follow-up error, with the result that the settling time cannot be made small.
In such a system that change-over is carried out from a speed control system to a position control system at a time point that a position deviation is a constant value or less, there is further a problem that the change-over is possible in the vicinity of a desired position deviation, but a strong decelerating action in the speed control system causes a head speed to be decelerated too much down to a stall state, thus resulting in an increase of a time taken for the head to reach the target track position, with a prolonged access time.
In accordance with an aspect of the present invention, there is provided a means for causing a position controller to generate a drive signal of a linear or primary function of time when the a position deviation signal becomes zero at a desired finite settling time in such a manner that, immediately after a switching judger changes over from a speed controller to the position controller as a positioning compensator, the position deviation signal responds to it in the form of a ternary-order function of time when the position deviation signal becomes zero at the desired finite settling time; or there is provided a means for causing the position controller to generate a drive signal of an (m+1)-order function of time when the position deviation signal becomes zero at a desired finite settling time in such a manner that the position deviation signal responds to it in the form of an (m+3)-order function (where, m being a natural number) when the position deviation signal becomes zero at a desired finite settling time, whereby the infinite settling time can be made zero.
In the aspect of the present invention, there is provided a recording and reproducing device which includes a target position signal generator for calculating and outputting a target position signal of a ternary-order function of time when a position deviation signal becomes zero in a desired settling time with an inverted value of the position deviation signal as an initial value immediately after change-over to a position controller; a feedforward signal generator for calculating and outputting a feedforward signal of a linear function of time when the position deviation signal becomes zero in the desired settling time with a proportional value of the position deviation signal immediately after change-over to a positioning controller as an initial value; a first adder for adding a target position signal to the position deviation signal and outputting it as a new position deviation signal; a second adder for adding the feedforward signal to a drive signal as an output of a positioning compensator and outputting it as a new drive signal; and an initial value setter for causing state variables of the positioning compensator to be cleared to zeros before the positioning compensator receives the position deviation signal. In this case, since a means is provided for causing feedforward compensation to improve a follow-up performance to the target position signal, a follow-up error to the target position signal can be reduced and a settling time can be shortened.
The target position signal of the ternary-order function and the feedforward signal of the linear function may be replaced by higher-order functions which follow. When the higher-order functions are employed, there is provided a means for calculating and outputting a target position signal of an (m+3)-order function (where, m being a natural number) of time when the position deviation signal becomes zero in the settling time with an inverted value of the position deviation signal immediately after change-over to the position controller as an initial value, and for calculating and outputting a feedforward signal of an (m+1)-order function of time when the feedforward signal becomes zero in a settling time with a proportional value of the position deviation signal immediately after change-over to the positioning controller as an initial value.
Further, a switching judger in the present invention starts its judging operation after the position deviation signal reaches its predetermined position deviation level, performs its switching operation from the speed controller to the position controller when the position deviation signal becomes a value corresponding to a proportional multiple of that of a speed signal, whereby a speed control system prevents an increase of the settling time caused by stall of a head speed and thus variations in a time taken for change-over from the speed controller to the position controller can be stabilized. As a result, a change-over time from the speed controller to the position controller can be stabilized.